Principles and potential of the anaerobic digestion of waste-activated sludge

Lignocelluloses are often a major or sometimes the sole components of different waste streams from various industries, forestry, agriculture and municipalities. Hydrolysis of these materials is the first step for either digestion to biogas (methane) or fermentation to ethanol. However, enzymatic hydrolysis of lignocelluloses with no pretreatment is usually not so effective because of high stability of the materials to enzymatic or bacterial attacks. The present work is dedicated to reviewing the methods that have been studied for pretreatment of lignocellulosic wastes for conversion to ethanol or biogas. Effective parameters in pretreatment of lignocelluloses, such as crystallinity, accessible surface area, and protection by lignin and hemicellulose are described first. Then, several pretreatment methods are discussed and their effects on improvement in ethanol and/or biogas production are described. They include milling, irradiation, microwave, steam explosion, ammonia fiber explosion (AFEX), supercritical CO2 and its explosion, alkaline hydrolysis, liquid hot-water pretreatment, organosolv processes, wet oxidation, ozonolysis, dilute- and concentrated-acid hydrolyses, and biological pretreatments.

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Pretreatment of lignocellulosic wastes to improve ethanol and biogas production: a review.

http://repository.ias.ac.in/39608/1/49_pub.pdf

A review of imperative technologies for wastewater treatment I: oxidation technologies at ambient conditions

Trends in biotechnological production of fuel ethanol from different feedstocks.

Hydrothermal liquefaction of biomass: A review of subcritical water technologies

In recent years, growing attention has been devoted to the conversion of biomass into fuel ethanol, considered the cleanest liquid fuel alternative to fossil fuels. Significant advances have been made towards the technology of ethanol fermentation. This review provides practical examples and gives a broad overview of the current status of ethanol fermentation including biomass resources, microorganisms, and technology. Also, the promising prospects of ethanol fermentation are especially introduced. The prospects included are fermentation technology converting xylose to ethanol, cellulase enzyme utilized in the hydrolysis of lignocellulosic materials, immobilization of the microorganism in large systems, simultaneous saccharification and fermentation, and sugar conversion into ethanol.

Ethanol fermentation from biomass resources: current state and prospects.

Effects of thermochemical pretreatment on the anaerobic digestion of waste activated sludge

Fermentation of sugar by Saccharomyces cerevisiae BY4742, for production of ethanol in a batch experiment was conducted to improve the performance of the fermentation process. The thermotolerant ability of S. cerevisiae to grow and ferment glucose at elevated temperatures similar to the optima for saccharification was investigated. The influences of temperature, substrate concentration and pH on ethanol fermentation were observed. The yield for ethanol production and changes in the fermentation pathway were compared under different conditions. When the temperature was increased to 45 °C, the system still showed high cell growth and ethanol production rates, while it was inhibited at 50 °C. The maximum specific growth rate and the maximum specific ethanol production rate were observed between 30 and 45 °C with different initial glucose concentrations. The maximum sugar conversion at 30 °C after 72 h incubation was 48.0%, 59.9%, 28.3%, 13.7% and 3.7% for 20, 40, 80, 160 and 300 kg m⁻³ of glucose concentrations respectively. Increased substrate supply did not improve the specific ethanol production rate when the pH value was not controlled. pH 4.0–5.0 was the optimal range for the ethanol production process. The highest specific ethanol production rate for all the batch experiments was achieved at pH5.0 which is 410 g kg⁻¹ h⁻¹ of suspended solids (SS) which gave an ethanol conversion efficiency of 61.93%. The highest specific ethanol production rate at 4.0 was 310 g kg⁻¹ h⁻¹ of SS. A change in the main fermentation pathway was observed with various pH ranges. Formation of acetic acid was increased when the pH was below 4.0, while butyric acid was produced when the pH was higher than 5.0. In the presence of oxygen, the ethanol could be utilized by the yeast as the carbon source after other nutrients became depleted, this could not occur however under anaerobic conditions.

Factors affecting ethanol fermentation using Saccharomyces cerevisiae BY4742

The authors review presently available or potential biological methods to remove and detoxify toxic heavy metals and metalloids from polluted water and sediments (i.e., biosorption, bioaccumulation, oxidation/reduction, leaching, precipitation, volatilization, degradation, and phytoremediation). In addition, they describe the options for the recovery of metals sequestered by biosorbents (use of appropriate desorbing agents) and microbial and plant biomass (leaching by means of chemical reagents or biological processes, and thermal treatment in controlled systems).

Biological Removal and Recovery of Toxic Heavy Metals in Water Environment

A batch fermentation utilizing Saccharomyces cerevisiae BY4742 was conducted to determine the inhibitory effects of highly concentrated substrate and product levels on yeast. Experiments were performed to determine the largest dosage of substrate and the largest product concentration that the yeast could tolerate in a very high gravity fermentation process. The yeast’s growth and fermentation activities were characterized by changes in the biomass and ethanol yield under different substrate and product concentrations during fermentation. All of the experiments were performed at a pH of 5.0 and a temperature of 35 °C with a stirring rate of 180 r/min and a fermentation time of 96 h. Furthermore, five cycles of acclimatization were conducted to improve the yeast’s tolerance to ethanol. Ethanol yield was maximized at 95% with a product concentration of 39 g/L and substrate dosage of 80 g/L. The system exhibited an obvious increase in cell growth and ethanol production with increasing substrate dosage up to a...

Shuzo Tanaka

Papers

Ethanol fermentation from biomass resources: current state and prospects.

Effects of thermochemical pretreatment on the anaerobic digestion of waste activated sludge

Factors affecting ethanol fermentation using Saccharomyces cerevisiae BY4742

Biological Removal and Recovery of Toxic Heavy Metals in Water Environment

Substrate and Product Inhibition on Yeast Performance in Ethanol Fermentation